Going it alone: Cochineal insects (Dactylopiidae: Hemiptera) do not have an obligate nutritional symbiont

Phloem-feeding insects survive on plant sap that is deficient in essential amino acids. Almost all of these phloem-feeders have an obligate intracellular, maternally inherited symbiont that provision the insects with amino acids (a “primary” symbiont). Cochineal insects are iconic phloem-feeding New World bugs that feed on cactus. These insects are of economic and cultural significance as biological control agents of invasive cactus and as pests of beneficial cactus. This family also includes one species that has been domesticated for dye production. The domesticated species, Dactylopius coccus, has been cultivated as a source of red dye since the Aztec period. We investigated the 16S rRNA bacterial and and ITS fungal microbiome of cochineal species collected primarily in Arizona and Texas with some additional samples from the introduced range in South Africa and Israel. We found no single bacterium or fungus that was a good candidate to be a primary symbiont of Dactylopius. While the bacterium Dactylopiibacterium carminicum (Betaproteobacteria) was extremely abundant when it was present and had been nominated as the primary symbiont of cochineal in previous published work, D. carminicum was entirely absent from some insects, nor was any fungal candidate apparent. We also found no clear difference in the microbial community among species sampled. How these phloem-feeders survive without a primary symbiont is yet unclear, as is the role of the sometimes-abundant D. carminicum.